Cleaning effects in optical layers: error characteristics and analysis methods

In the course of the ever-increasing demand of high-performance optical components, dielectric coating processes are the key technology for the refinement of optics, ensuring their functionality. These optics are based on optical interference coatings, which are formed by a layer stack of alternating transparent single layers of high and low refractive index material. Assuming that turbidity as well as defects embedded in coatings are considered as a primary factor limiting the quality of optical coatings, the level of cleaning the substrates before coating has to be extremely high. Particular importance is attached to the interface between the layer stack and the substrate, especially to the interaction during the transition from the glass surface to the coating during the manufacturing process. This interaction is assumed to be caused by polishing, by corrosion during storage time or by effects during cleaning of the substrate before coating. Thus, it is necessary to characterize each type of defect and to define which technique is adequate to analyze each one of them efficiently. The project aims to raise the awareness and knowledge in terms of what happens during the coating process and, in particular, to understand the physical processes at the substrate during the manufacturing process. After analyzing the material flow, first focus was set on the cleaning procedure. It is assumed that one of the main influences on defects in the interface is the chemical cleaning. Chemical reactions on the surface of the glass substrate may occur due to additional effects of external components and elevated temperature in the washing basins.